The field of the present invention is camshaft drive gear trains and particularly those employed on transversely mounted four cycle engines.
Transversely mounted engines as may be employed in a small vehicle and particularly in motorcycles or the like must be compactly arranged for advantageous vehicle design. One such transversely mounted engine arrangement is illustrated in FIG. 1 as being a V-type four cylinder engine with the arrow indicating the forward direction on the vehicle. The cross hatched plane illustrated between cylinders in the bank of cylinders illustrates the location at which the camshaft drive trains are arranged. One such drive train arrangement is specifically illustrated in FIG. 2 as including a crankshaft 10, first idle gear wheels 12 and second idle gear wheels 14. Thus, two idle gear trains, each including a wheel 12 and a wheel 14 are driven off of the crankshaft 10. In turn, the idle gear trains each drive two camshafts 16 and 18.
In such transversely mounted engines, the main shaft of the transmission is generally arranged parallel to the crankshaft and adjacent thereto. A main shaft 20 is illustrated in FIG. 2 as being displaced through a distance L. The crankshaft 10 is normally coupled to the main shaft 20 through a clutch arrangement and appropriate gearing.
Because the main shaft 20 also includes gear wheels and the like, the distance between centerlines of the crankshaft 10 and the main shaft 20 must be arranged such that clearance is provided between the engine and transmission components. Thus, L is often larger than would otherwise be necessary to accommodate the drive train components between the crankshaft and the main shaft of the transmission. One specific interfering component is the idle gear train of a camshaft drive train and, in particular, the first idler gear wheel 12 as can be seen in FIG. 2. Thus, the idle gear train for the camshafts in a transversely mounted V-type engine can result in an inefficient arrangement of components resulting in increased size of the engine/transmission unit.
A further difficulty has been encountered in the employment of an idle gear train for driving overhead camshafts. Unless very close tolerances are maintained on the gear wheels and the idle gear retainer, gear backlash can become a problem. One solution is to prepare a great number of gears falling within a less restrictive tolerance requirement which are then matched according to their actual size for employment in a camshaft drive train. Such a procedure is expensive and time consuming.